<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>02_计算器</title>
</head>
<body>
<input type="text" placeholder="请输入数字1" id="i1"><br>
<input type="text" placeholder="请输入数字2" id="i2"><br>
<button onclick="calc('+')">加</button>
<button onclick="calc('-')">减</button>
<button onclick="calc('*')">乘</button>
<button onclick="calc('/')">除</button>
<h4>运算结果：<span></span></h4>
<script>
    //定义运算的方法
    function calc(o){
        let n1=document.querySelector('#i1').value;
        let n2=document.querySelector('#i2').value;
        n1 =parseFloat(n1);
        n2 =parseFloat(n2);
        let spanE=document.querySelector('span');
        switch (o) {
            case '+':
            spanE.innerHTML=n1+n2;break;
            case '-':
                spanE.innerHTML=n1-n2;break;
            case '*':
                spanE.innerHTML=n1*n2;break;
            case '/':
                if(n2!=0){
                    spanE.innerHTML= n1 / n2;
                }else {
                    alert('除数不能为0！');
                }
        }
    }
</script>
</body>
</html>